Immersion-cooled and conduction-cooled electronic system

ABSTRACT

A cooled electronic system and cooling method are provided, where an electronics board having a plurality of electronic components mounted to the board is cooled by an apparatus which includes an immersion-cooled electronic component section and a conduction-cooled electronic component section. The immersion-cooled section includes an enclosure at least partially surrounding and forming a compartment about multiple electronic components of the electronic components mounted to the electronics board, and a fluid disposed within the compartment. The multiple electronic components are, at least in part, immersed within the fluid to facilitate immersion-cooling of those components. The conduction-cooled electronic component section includes at least one electronic component of the electronic components mounted to the electronics board, and the at least one electronic component is indirectly liquid-cooled, at least in part, via conduction of heat from the at least one electronic component.

BACKGROUND

The power dissipation of integrated circuit chips, and the modulescontaining the chips, continues to increase in order to achieveincreases in processor performance. This trend poses cooling challengesat the module and system levels.

In many large server applications, processors along with theirassociated electronics (e.g., memory, disk drives, power supplies, etc.)are packaged in removable drawer configurations stacked within anelectronics rack or frame comprising information technology (IT)equipment. In other cases, the electronics may be in fixed locationswithin the rack or frame. Typically, the components are cooled by airmoving in parallel airflow paths, usually front-to-back, impelled by oneor more air moving devices (e.g., fans or blowers). In some cases it maybe possible to handle increased power dissipation within a single draweror subsystem by providing greater airflow, for example, through the useof a more powerful air moving device or by increasing the rotationalspeed (i.e., RPMs) of an existing air moving device. However, thisapproach is becoming problematic, particularly in the context of acomputer center installation (i.e., data center).

The sensible heat load carried by the air exiting the rack is stressingthe capability of the room air-conditioning to effectively handle theload. This is especially true for large installations with “serverfarms” or large banks of computer racks located close together. In suchinstallations, liquid-cooling is an attractive technology to manage thehigher heat fluxes. The liquid absorbs the heat dissipated by thecomponents/modules in an efficient manner. Typically, the heat isultimately transferred from the liquid to an outside environment,whether air or other liquid.

BRIEF SUMMARY

The shortcomings of the prior art are overcome, and additionaladvantages are provided through the provision of a cooled electronicsystem which includes, for instance, an electronics board comprising aplurality of electronic components mounted to the electronics board, anda cooling apparatus facilitating cooling of the plurality of electroniccomponents mounted to the electronics board. The cooling apparatusincludes an immersion-cooled electronic component section, and aconduction-cooled electronic component section. The immersion-cooledelectronic component section includes: an enclosure at least partiallysurrounding and forming a compartment about multiple electroniccomponents of the plurality of electronic components mounted to theelectronics board; and a fluid disposed within the compartment, themultiple electronic components being, at least partially, immersedwithin the fluid to facilitate immersion-cooling thereof. Theconduction-cooled electronic component section includes at least oneelectronic component of the plurality of electronic components mountedto the electronics board, and the at least one electronic component isindirectly liquid-cooled, at least in part, via conduction of heat fromthe at least one electronic component.

In another aspect, a liquid-cooled electronics rack is provided whichincludes an electronics rack having at least one electronic system, theat least one electronic system including an electronics board comprisinga plurality of electronic components mounted to the electronics board.The liquid-cooled electronics rack further includes a cooling apparatuswhich comprises an immersion-cooled electronic component section and aconduction-cooled electronic component section. The immersion-cooledelectronic component section includes: an enclosure at least partiallysurrounding and forming a compartment about multiple electroniccomponents of the plurality of electronic components mounted to theelectronics board; and a fluid disposed within the compartment, themultiple electronic components being, at least partially, immersedwithin the fluid to facilitate immersion-cooling thereof. Theconduction-cooled electronic component section includes at least oneelectronic component of the plurality of electronic components mountedto the electronics board, and the at least one electronic component isindirectly liquid-cooled, at least in part, via conduction of heat fromthe at least one electronic component.

In a further aspect, a method of facilitating cooling of an electronicsystem is provided. The method includes providing a cooling apparatusfor cooling an electronics board of the electronic system, theelectronics board comprising a plurality of electronic componentsmounted to the electronics board. The cooling apparatus includes animmersion-cooled electronic component section, and a conduction-cooledelectronic component section. The immersion-cooled electronic componentsection includes: an enclosure at least partially surrounding andforming a compartment about multiple electronic components of theplurality of electronic components mounted to the electronics board; anda fluid disposed within the compartment, the multiple electroniccomponents being, at least partially, immersed within the fluid tofacilitate immersion-cooling thereof. The conduction-cooled electroniccomponent section includes at least one electronic component of theplurality of electronic components mounted to the electronics board, andthe at least one electronic component is indirectly liquid-cooled, atleast in part, via conduction of heat from the at least one electroniccomponent.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of a conventional raised floor layout ofan air-cooled computer installation;

FIG. 2 is a front elevational view of one embodiment of a liquid-cooledelectronics rack comprising multiple electronic systems to be cooled viaa cooling apparatus, in accordance with one or more aspects of thepresent invention;

FIG. 3 is a schematic of an electronic system of an electronics rack andone approach to liquid-cooling of an electronic component with theelectronic system, wherein the electronic component is indirectlyliquid-cooled by system coolant provided by one or more modular coolingunits disposed within the electronics rack, in accordance with one ormore aspects of the present invention;

FIG. 4 is a schematic of one embodiment of a modular cooling unit for aliquid-cooled electronics rack such as illustrated in FIG. 2, inaccordance with one or more aspects of the present invention;

FIG. 5 is a plan view of one embodiment of an electronic system layoutillustrating an air and liquid-cooling approach for cooling electroniccomponents of the electronic system, in accordance with one or moreaspects of the present invention;

FIG. 6A is an elevational view of an alternate embodiment of aliquid-cooled electronics rack with immersion-cooling of electronicsystems thereof, in accordance with one or more aspects of the presentinvention;

FIG. 6B is a cross-sectional elevational view of one immersion-cooledelectronic system of the liquid-cooled electronics rack of FIG. 6A, inaccordance with one or more aspects of the present invention;

FIG. 7A is a cross-sectional elevational view of one embodiment of acooled electronic system comprising a cooling apparatus includingimmersion-cooled and conduction-cooled electronic component sections,taken along line 7A-7A in the plan view of FIG. 7B, in accordance withone or more aspects of the present invention;

FIG. 7B is a cross-sectional plan view of the cooled electronic systemof FIG. 7A, taken along line 7B-7B thereof, in accordance with one ormore aspects of the present invention;

FIG. 8A is a cross-sectional elevational view of another embodiment of acooled electronic system comprising a cooling apparatus includingimmersion-cooled and conduction-cooled electronic component sections,taken along line 8A-8A in the plan view of FIG. 8B, in accordance withone or more aspects of the present invention;

FIG. 8B is a cross-sectional plan view of the cooled electronic systemof FIG. 8A, taken along line 8B-8B thereof, in accordance with one ormore aspects of the present invention;

FIG. 8C is a partial cross-sectional elevational view of the cooledelectronic system of FIGS. 8A & 8B, taken along line 8C-8C in the planview of FIG. 8B, in accordance with one or more aspects of the presentinvention;

FIG. 9A is a cross-sectional elevational view of another embodiment of acooled electronic system comprising a cooling apparatus includingimmersion-cooled and conduction-cooled electronic component sections,and taken along line 9A-9A in the plan view of FIG. 9B, in accordancewith one or more aspects of the present invention;

FIG. 9B is a cross-sectional plan view of the cooled electronic systemof FIG. 9A, taken along line 9B-9B thereof, in accordance with one ormore aspects of the present invention; and

FIG. 9C is a partial cross-sectional elevational view of the cooledelectronic system of FIGS. 9A & 9B, taken along line 9C-9C in the planview of FIG. 9B, in accordance with one or more aspects of the presentinvention.

DETAILED DESCRIPTION

As used herein, the terms “electronics rack”, “rack-mounted electronicequipment”, and “rack unit” are used interchangeably, and unlessotherwise specified include any housing, frame, rack, compartment, bladeserver system, etc., having one or more heat-generating components of acomputer system, electronic system, or information technology equipment,and may be, for example, a stand alone computer processor having high-,mid- or low-end processing capability. In one embodiment, an electronicsrack may comprise a portion of an electronic system, a single electronicsystem, or multiple electronic systems, for example, in one or moresub-housings, blades, books, drawers, nodes, compartments, etc., havingone or more heat-generating electronic components disposed therein. Anelectronic system(s) within an electronics rack may be movable or fixed,relative to the electronics rack, with rack-mounted electronic drawersand blades of a blade center system being two examples of electronicsystems (or subsystems) of an electronics rack to be cooled.

“Electronic component” refers to any heat generating electroniccomponent of, for example, a computer system or other electronics unitrequiring cooling. By way of example, an electronic component maycomprise one or more integrated circuit dies and/or other electronicdevices to be cooled, including one or more processor dies, memory diesor memory support dies. As a further example, the electronic componentmay comprise one or more bare dies or one or more packaged dies disposedon a common carrier. Further, unless otherwise specified herein, theterms “liquid-cooled cold plate”, “liquid-cooled structure”, or“liquid-cooled vapor condenser” each refer to a thermally conductivestructure having one or more channels or passageways formed therein forflowing of liquid-coolant therethrough.

As used herein, a “liquid-to-liquid heat exchanger” may comprise, forexample, two or more coolant flow paths, formed of thermally conductivetubing (such as copper or other tubing) in thermal or mechanical contactwith each other. Size, configuration and construction of theliquid-to-liquid heat exchanger can vary without departing from thescope of the invention disclosed herein. Further, “data center” refersto a computer installation containing one or more electronics racks tobe cooled. As a specific example, a data center may include one or morerows of rack-mounted computing units, such as server units.

By way of further explanation, a “heat pipe” is a heat transfer devicewhich combines the principles of both thermal conductivity and phasetransition to effectively manage transfer of heat. A simple type of heatpipe includes a sealed case, an inner surface of which is covered with alayer of capillary or porous material, or structure comprising a wickwhich is saturated with the working fluid in its liquid phase. At a hotinterface within the heat pipe, which may be at a low pressure, aworking fluid within the heat pipe in contact with a thermallyconductive surface (for example, an inner wall of the casing or a wick),turns into a vapor by absorbing heat from that surface. The workingfluid vapor condenses back into a liquid at a cold interface of the heatpipe, releasing the latent heat. The working fluid liquid then returnsto the hot interface through, for example, the wick structure bycapillary action or gravity, where it evaporates once more and repeatsthe cycle. Internal pressure within the heat pipe can be set or adjustedto facilitate the phase change, depending on the demands of the workingconditions of the cooling system.

One example of facility coolant and system coolant is water. However,the concepts disclosed herein are readily adapted to use with othertypes of coolant on the facility side and/or on the system side. Forexample, one or more of these coolants may comprise a brine, adielectric liquid, a fluorocarbon liquid, a liquid metal, or othersimilar coolant, or a refrigerant, while still maintaining theadvantages and unique features of the present invention.

Reference is made below to the drawings (which are not drawn to scale tofacilitate an understanding of the various aspects of the presentinvention), wherein the same reference numbers used throughout differentfigures designate the same or similar components.

As shown in FIG. 1, in a raised floor layout of an air-cooled datacenter 100 typical in the prior art, multiple electronics racks 110 aredisposed in one or more rows. A computer installation such as depictedin FIG. 1 may house several hundred, or even several thousandmicroprocessors. In the arrangement of FIG. 1, chilled air enters thecomputer room via floor vents from a supply air plenum 145 definedbetween the raised floor 140 and a base or sub-floor 165 of the room.Cooled air is taken in through louvered covers at air inlet sides 120 ofthe electronics racks and expelled through the backs, i.e., air outletsides 130, of the electronics racks. Each electronics rack 110 may haveone or more air-moving devices (e.g., fans or blowers) to provide forcedinlet-to-outlet air flow to cool the electronic components within thedrawer(s) of the rack. The supply air plenum 145 provides conditionedand cooled air to the air-inlet sides of the electronics racks viaperforated floor tiles 160 disposed in a “cold” aisle of the computerinstallation. The conditioned and cooled air is supplied to plenum 145by one or more air conditioning units 150, also disposed within datacenter 100. Room air is taken into each air conditioning unit 150 nearan upper portion thereof. This room air may comprise (in part) exhaustedair from the “hot” aisles of the computer installation defined byopposing air outlet sides 130 of the electronics racks 110.

FIG. 2 depicts one embodiment of a liquid-cooled electronics rack 200comprising a cooling apparatus. In one embodiment, liquid-cooledelectronics rack 200 comprises a plurality of electronic systems 210,which may be processor or server nodes (in one embodiment). A bulk powerassembly 220 is disposed at an upper portion of liquid-cooledelectronics rack 200, and two modular cooling units (MCUs) 230 arepositioned in a lower portion of the liquid-cooled electronics rack forproviding system coolant to the electronic systems. In the embodimentsdescribed herein, the system coolant is assumed to be water or anaqueous-based solution, by way of example only.

In addition to MCUs 230, the cooling apparatus depicted includes asystem coolant supply manifold 231, a system coolant return manifold232, and manifold-to-node fluid connect hoses 233 coupling systemcoolant supply manifold 231 to electronic subsystems 210 (for example,to cold plates or liquid-cooled vapor condensers (see FIGS. 6A-9B)disposed within the systems) and node-to-manifold fluid connect hoses234 coupling the individual electronic systems 210 to system coolantreturn manifold 232. Each MCU 230 is in fluid communication with systemcoolant supply manifold 231 via a respective system coolant supply hose235, and each MCU 230 is in fluid communication with system coolantreturn manifold 232 via a respective system coolant return hose 236.

Heat load of the electronic systems 210 is transferred from the systemcoolant to cooler facility coolant within the MCUs 230 provided viafacility coolant supply line 240 and facility coolant return line 241disposed, in the illustrated embodiment, in the space between raisedfloor 145 and base floor 165.

FIG. 3 schematically illustrates one cooling approach using the coolingapparatus of FIG. 2, wherein a liquid-cooled cold plate 300 is showncoupled to an electronic component 301 of an electronic system 210within the liquid-cooled electronics rack 200. Heat is removed fromelectronic component 301 via system coolant circulating via pump 320through liquid-cooled cold plate 300 within the system coolant loopdefined, in part, by liquid-to-liquid heat exchanger 321 of modularcooling unit 230, hoses 235, 236 and cold plate 300. The system coolantloop and modular cooling unit are designed to provide coolant of acontrolled temperature and pressure, as well as controlled chemistry andcleanliness to the electronic systems. Furthermore, the system coolantis physically separate from the less controlled facility coolant inlines 240, 241, to which heat is ultimately transferred.

FIG. 4 depicts one detailed embodiment of a modular cooling unit 230. Asshown in FIG. 4, modular cooling unit 230 includes a facility coolantloop, wherein building chilled, facility coolant is provided (via lines240, 241) and passed through a control valve 420 driven by a motor 425.Valve 420 determines an amount of facility coolant to be passed throughheat exchanger 321, with a portion of the facility coolant possiblybeing returned directly via a bypass orifice 435. The modular coolingunit further includes a system coolant loop with a reservoir tank 440from which system coolant is pumped, either by pump 450 or pump 451,into liquid-to-liquid heat exchanger 321 for conditioning and outputthereof, as cooled system coolant to the electronics rack to be cooled.Each modular cooling unit is coupled to the system supply manifold andsystem return manifold of the liquid-cooled electronics rack via thesystem coolant supply hose 235 and system coolant return hose 236,respectively.

FIG. 5 depicts another cooling approach, illustrating one embodiment ofan electronic system 210 component layout wherein one or more air movingdevices 511 provide forced air flow 515 in normal operating mode to coolmultiple electronic components 512 within electronic system 210. Coolair is taken in through a front 531 and exhausted out a back 533 of thedrawer. The multiple components to be cooled include multiple processormodules to which liquid-cooled cold plates 520 are coupled, as well asmultiple arrays of memory modules 530 (e.g., dual in-line memory modules(DIMMs)) and multiple rows of memory support modules 532 (e.g., DIMMcontrol modules) to which air-cooled heat sinks may be coupled. In theembodiment illustrated, memory modules 530 and the memory supportmodules 532 are partially arrayed near front 531 of electronic system210, and partially arrayed near back 533 of electronic system 210. Also,in the embodiment of FIG. 5, memory modules 530 and the memory supportmodules 532 are cooled by air flow 515 across the electronics system.

The illustrated cooling apparatus further includes multiplecoolant-carrying tubes connected to and in fluid communication withliquid-cooled cold plates 520. The coolant-carrying tubes comprise setsof coolant-carrying tubes, with each set including (for example) acoolant supply tube 540, a bridge tube 541 and a coolant return tube542. In this example, each set of tubes provides liquid-coolant to aseries-connected pair of cold plates 520 (coupled to a pair of processormodules). Coolant flows into a first cold plate of each pair via thecoolant supply tube 540 and from the first cold plate to a second coldplate of the pair via bridge tube or line 541, which may or may not bethermally conductive. From the second cold plate of the pair, coolant isreturned through the respective coolant return tube 542.

As computing demands continue to increase, heat dissipation requirementsof electronic components, such as microprocessors and memory modules,are also rising. This has motivated the development of the applicationof single-phase, liquid-cooling solutions such as described above.Single-phase, liquid-cooling, however, has some issues. Sensible heatingof the liquid as it flows along the cooling channels and acrosscomponents connected in series results in a temperature gradient. Tomaintain a more uniform temperature across the heat-generatingcomponent, the temperature change in the liquid needs to be minimized.This requires the liquid to be pumped at higher flow rates, consumingmore pump power, and thus leading to a less efficient system. Further,it is becoming increasingly challenging to cool all the heat sources ona server or electronic system using pumped liquid, due to the densityand number of components, such as controller chips, I/O components andmemory modules. The small spaces and number of components to be cooledmake liquid plumbing a complex design and fabrication problem andsignificantly raises the overall cost of the cooling solution.

Immersion-cooling is one possible solution to these issues. Inimmersion-cooling, typically all components to be cooled are immersed ina dielectric fluid that dissipates heat through boiling. The vapor isthen condensed by a secondary, rack-level working (or system) fluidusing node or module-level, finned condensers, as explained below.

Direct immersion-cooling of electronic components of an electronicsystem of the rack unit using dielectric fluid (e.g., a liquiddielectric coolant) advantageously avoids forced air cooling and enablestotal liquid-cooling of the electronics rack within the data center.Although indirect liquid-cooling, such as described above in connectionwith FIGS. 3 and 5, has certain advantages due to the low cost and wideavailability of water as a coolant, as well as its superior thermal andhydraulic properties, where possible and viable, the use of dielectricfluid immersion-cooling may offer several unique benefits.

For example, the use of a dielectric fluid that condenses at atemperature above typical outdoor ambient air temperature would enabledata center cooling architectures which do not require energy intensiverefrigeration chillers. Also, the use of liquid immersion-cooling may,in certain cases, allow for greater compaction of electronic componentsat the electronic subsystem level and/or electronic rack level sinceconductive cooling structures might be eliminated. Unlike corrosionsensitive water-cooled systems, chemically inert dielectric coolant(employed with an immersion-cooling approach such as described herein)would not mandate copper as the primary thermally conductive wettedmetal. Lower cost and lower mass aluminum structures could replacecopper structures wherever thermally viable, and the mixed wetted metalassemblies would not be vulnerable to galvanic corrosion, such as in thecase of a water-based cooling approach. For at least these potentialbenefits, dielectric fluid immersion-cooling of one or more electronicsystems (or portions of one or more electronic systems) of anelectronics rack may offer significant energy efficiency and higherperformance cooling benefits, compared with currently available hybridair and indirect water cooled systems.

In the examples discussed below, the dielectric fluid may comprise anyone of a variety of commercially available dielectric coolants. Forexample, any of the Fluorinert™ or Novec™ fluids manufactured by 3MCorporation (e.g., FC-72, FC-86, HFE-7000, and HFE-7200) could beemployed. Alternatively, a refrigerant such as R-134a or R-245fa may beemployed if desired.

FIG. 6A is a schematic of one embodiment of a liquid-cooled electronicsrack, generally denoted 600, employing immersion-cooling of electronicsystems, in accordance with an aspect of the present invention. Asshown, liquid-cooled electronics rack 600 includes an electronics rack601 containing a plurality of electronic systems 610 disposed, in theillustrated embodiment, horizontally so as to be stacked within therack. By way of example, each electronic system 610 may be a server unitof a rack-mounted plurality of server units. In addition, eachelectronic system includes multiple electronic components to be cooled,which in one embodiment, comprise multiple different types of electroniccomponents having different heights and/or shapes within the electronicsystem.

The cooling apparatus is shown to include one or more modular coolingunits (MCU) 620 disposed, by way of example, in a lower portion ofelectronics rack 601. Each modular cooling unit 620 may be similar tothe modular cooling unit depicted in FIG. 4, and described above. Themodular cooling unit includes, for example, a liquid-to-liquid heatexchanger for extracting heat from coolant flowing through a systemcoolant loop 630 of the cooling apparatus and dissipating heat within afacility coolant loop 619, comprising a facility coolant supply line 621and a facility coolant return line 622. As one example, facility coolantsupply and return lines 621, 622 couple modular cooling unit 620 to adata center facility coolant supply and return (not shown). Modularcooling unit 620 further includes an appropriately sized reservoir, pumpand optional filter for moving liquid-coolant under pressure throughsystem coolant loop 630. In one embodiment, system coolant loop 630includes a coolant supply manifold 631 and a coolant return manifold632, which are coupled to modular cooling unit 620 via, for example,flexible hoses. The flexible hoses allow the supply and return manifoldsto be mounted within, for example, a door of the electronics rackhingedly mounted to the front or back of the electronics rack. In oneexample, coolant supply manifold 631 and coolant return manifold 632each comprise an elongated rigid tube vertically mounted to theelectronics rack 601 or to a door of the electronics rack.

In the embodiment illustrated, coolant supply manifold 631 and coolantreturn manifold 632 are in fluid communication with respective coolantinlets 635 and coolant outlets 636 of individual sealed housings 640containing the electronic systems 610. Fluid communication between themanifolds and the sealed housings is established, for example, viaappropriately sized, flexible hoses 633, 634. In one embodiment, eachcoolant inlet 635 and coolant outlet 636 of a sealed housing is coupledto a respective liquid-cooled vapor condenser 650 disposed within thesealed housing 640. Heat removed from the electronic system 610 via therespective liquid-cooled vapor condenser 650 is transferred from thesystem coolant via the coolant return manifold 632 and modular coolingunit 620 to facility coolant loop 619. In one example, coolant passingthrough system coolant loop 630, and hence, coolant passing through therespective liquid-cooled vapor condensers 650 is water.

Note that, in general, fluidic coupling between the electronicsubsystems and coolant manifolds, as well as between the manifolds andthe modular cooling unit(s) can be established using suitable hoses,hose barb fittings and quick disconnect couplers. In the exampleillustrated, the vertically-oriented coolant supply and return manifolds631, 632 each include ports which facilitate fluid connection of therespective coolant inlets and outlets 635, 636 of the housings(containing the electronic subsystems) to the manifolds via the flexiblehoses 633, 634. Respective quick connect couplings may be employed tocouple the flexible hoses to the coolant inlets and coolant outlets ofthe sealed housings to allow for, for example, removal of a housing andelectronic subsystem from the electronics rack. The quick connectcouplings may be any one of various types of commercial availablecouplings, such as those available from Colder Products Co. of St. Paul,Minn., USA or Parker Hannifin of Cleveland, Ohio, USA.

One or more hermetically sealed electrical connectors 648 may also beprovided in each sealed housing 640, for example, at a back surfacethereof, for docking into a corresponding electrical plane of theelectronics rack in order to provide electrical and network connections649 to the electronic system disposed within the sealed housing when theelectronic system is operatively positioned within the sealed housingand the sealed housing is operatively positioned within the electronicsrack.

As illustrated in FIG. 6B, electronic system 610 comprises a pluralityof electronic components 642, 643 of different height and type on asubstrate 641, and is shown within sealed housing 640 with the pluralityof electronic components 642, 643 immersed within a dielectric fluid645. Sealed housing 640 is configured to at least partially surround andform a sealed compartment about the electronic system with the pluralityof electronic components 642, 643 disposed within the sealedcompartment. In an operational state, dielectric fluid 645 pools in theliquid state at the bottom of the sealed compartment and is ofsufficient volume to submerge the electronic components 642, 643. Theelectronic components 642, 643 dissipate varying amounts of power, whichcause the dielectric fluid to boil, releasing dielectric fluid vapor,which rises to the upper portion of the sealed compartment of thehousing.

The upper portion of sealed housing 640 is shown in FIG. 6B to includeliquid-cooled vapor condenser 650. Liquid-cooled vapor condenser 650 isa thermally conductive structure which includes a liquid-cooled baseplate 652, and a plurality of thermally conductive condenser fins 651extending therefrom in the upper portion of the sealed compartment. Aplenum structure 654 comprises part of liquid-cooled base plate 652, andfacilitates passage of system coolant through one or more channels inthe liquid-cooled base plate 652. In operation, the dielectric fluidvapor contacts the cool surfaces of the thermally conductive condenserfins and condenses back to liquid phase, dropping downwards towards thebottom of the sealed compartment.

System coolant supplied to the coolant inlet of the housing passesthrough the liquid-cooled base plate of the liquid-cooled vaporcondenser and cools the solid material of the condenser such thatcondenser fin surfaces that are exposed within the sealed compartment tothe dielectric fluid vapor (or the dielectric fluid itself) are wellbelow saturation temperature of the vapor. Thus, vapor in contact withthe cooler condenser fin surfaces will reject heat to these surfaces andcondense back to liquid form. Based on operating conditions of theliquid-cooled vapor condenser 650, the condensed liquid may be close intemperature to the vapor temperature or could be sub-cooled to a muchlower temperature.

Advantageously, in immersion-cooling such as depicted in FIGS. 6A & 6B,all of the components to be cooled are immersed in the dielectric fluid.The system fluid can tolerate a larger temperature rise, whilemaintaining component temperatures, thus allowing a smaller flow rate,and higher inlet temperatures, improving energy efficiency of theresultant cooling apparatus.

Immersion-cooling of an electronic system, such as a server, may presentproblems with regards to servicing or replacing in the field one or moreof the components of the electronic system, such as one or more memorymodules. Servicing/replacing a component with an immersion-cooledelectronic system approach, such as described above in connection withFIGS. 6A & 6B, requires that the electronic system be drained, and thatthe sealed enclosure be opened to access the electronic component(s) tobe serviced or replaced. This can be a time consuming and costlyprocedure.

In accordance with the cooled electronic systems presented herein,examples of which are depicted in FIGS. 7A-9C, a hybrid cooling approachis disclosed, wherein the cooling apparatus includes both animmersion-cooled electronic component section and a conduction-cooledelectronic component section, with the one or more electronic componentswithin the conduction-cooled electronic component section beingfield-replaceable, without requiring draining and opening of the sealedenclosure defining the immersion-cooled electronic component section.

Generally stated, a cooled electronic system is disclosed herein, wherean electronics board of the cooled electronic system includes aplurality of electronic components mounted to the board, and a coolingapparatus facilitates cooling of the plurality of electronic components.The cooling apparatus includes an immersion-cooled electronic componentsection and a conduction-cooled electronic component section. Within theimmersion-cooled electronic component section, an enclosure at leastpartially surrounds and forms a compartment about multiple electroniccomponents of the plurality of electronic components mounted to theelectronics board, and a fluid, that is, a dielectric fluid, is disposedwithin the compartment, and the multiple electronic components are, atleast partially, immersed within the fluid to facilitateimmersion-cooling thereof. The conduction-cooled electronic componentsection includes at least one electronic component of the plurality ofelectronic components mounted to the electronics board, and the at leastone electronic component within this section is indirectlyliquid-cooled, at least in part, via conduction of heat from the atleast one electronic component. Advantageously, the at least oneelectronic component is field-replaceable, without draining the fluidand opening the enclosure of the immersion-cooled electronic componentsection. In one specific example, the at least one electronic componentof the conduction-cooled electronic component section includes one ormore dual-in-line memory modules (DIMMs), which may be readily accessedand field-replaced or serviced.

By way of further example, in the hybrid cooling approach disclosedherein, a region (or section) of an electronic system or electronicsboard which includes one or more field-replaceable components, such asDIMMs, remains outside of the immersion-cooled electronic componentsection, and more particularly, the enclosure of that section, whereasthe balance of the plurality of electronic components mounted to theelectronics board are within the immersion-cooled electronic componentsection and cooled, at least in part, by vaporization of dielectricfluid within the sealed compartment of the immersion-cooled section. Thefield-replaceable components are instead conduction-cooled, forinstance, using any of a variety of conduction-cooling approaches suchas described herein.

A first approach is to employ heat pipes disposed in between theelectronic components of the conduction-cooled electronic componentsection, to make thermal contact with the heated electronic components,and thermally couple the components to the enclosure of theimmersion-cooled electronic component section, where the heat conductedaway from the field-replaceable electronic component(s) is convectedfrom the enclosure to the dielectric fluid within the immersion-cooledelectronic component section. One embodiment of this approach isdepicted in FIGS. 7A & 7B.

In another approach, depicted in FIGS. 8A-8C, heat is conducted awayfrom the field-replaceable electronic components of theconduction-cooled electronic component section employing one or morefluid-containing channels formed integral with, or coupled to, theenclosure of the immersion-cooled electronic component section, and influid communication with the compartment of the immersion-cooledelectronic component section such that the fluid within the compartmentof the immersion-cooled electronic component section is also disposedwithin the fluid channel(s). Heat from the electronic component(s) ofthe conduction-cooled electronic component section is thermallyconducted to the fluid-containing channels, and by convection, to thefluid within the fluid channel(s), causing the dielectric fluid tovaporize, and the fluid vapor to be transported to the compartment ofthe immersion-cooled electronic component section, to be condensed backto liquid.

In both of these approaches, the electronic components of theconduction-cooled electronic component section, such as DIMMs, may bedesigned to be field-replaceable and can be readily inserted into orremoved from (for instance) respective sockets mounted to theelectronics board, since they are outside of the enclosure of theimmersion-cooled electronic component section.

In another approach, depicted in FIGS. 9A-9C, a separable liquid-cooledcold plate is provided in association with the conduction-cooledelectronic component section. This separate, separable liquid-cooledcold plate is, in one embodiment, fluidically connected to theliquid-cooled vapor condenser associated with the enclosure of theimmersion-cooled electronic component section. In one implementation,the separable, liquid-cooled cold plate includes thermally conductivefins, such as coolant-carrying fin structures, which extend downwards,in-between the field-replaceable electronic components (such as DIMMs)mounted to the electronics board. Heat generated by these electroniccomponents is thermally conducted to the liquid-cooled cold plate, wherethe heat is transferred by convection to liquid coolant flowing throughthe liquid-cooled cold plate. In one example, this liquid coolant maycomprise water.

An advantage of the hybrid cooling apparatuses disclosed herein is theability to readily insert and remove certain, designatedfield-replaceable, electronic components (such as DIMMs), from anelectronic system, which is also (for example, mostly) enclosed by animmersion-cooling enclosure. This reduces the cost and time associatedwith replacing the electronic component(s) of the conduction-cooledelectronic component section, compared with a cooling apparatuscomprising a fully-encapsulated, immersion-cooled electronic componentsystem, such as described above in connection with FIGS. 6A & 6B.

As noted, FIGS. 7A & 7B depict one embodiment of a cooled electronicsystem, generally denoted 700, in accordance with one or more aspects ofthe present invention. Referring collectively to FIGS. 7A & 7B, cooledelectronic system 700 includes an electronic system comprising anelectronics board 701, with a plurality of electronic components 702,703, 704, mounted thereto. A cooling apparatus is provided whichincludes an immersion-cooled electronic component section 710, and aconduction-cooled electronic component section 720.

As illustrated, immersion-cooled electronic component section 710includes an enclosure (or immersion-cooling enclosure) 711, which issealed via a gasket or other suitable sealing mechanism 712 toelectronics board 701, so as to define a fluid-tight compartment 713,which comprises a dielectric fluid 714, such as described above inconnection with the immersion-cooling approach of FIGS. 6A & 6B. Aliquid-cooled vapor condenser 715 is associated with or integrated withenclosure 711, for instance, in an upper portion thereof, and comprisesone or more liquid-carrying channels 716, and a plurality of thermallyconductive fins 717 extending into compartment 713 of immersion-cooledelectronic component section 710.

As illustrated in FIG. 7B, in one embodiment, the immersion-cooledelectronic component section 710 encircles the conduction-cooledelectronic component section 720. Within the conduction-cooledelectronic component section 720, one or more electronic components 703are mounted to electronics board 701, for instance, via respectivesockets 705. In one example, the electronic components 703 ofconduction-cooled electronic component section 720 may comprise DIMMs,each with a plurality of memory modules 704 mounted on opposite sidesthereof. Within conduction-cooled electronic component section 720,electronic components 703 are thermally coupled to respective heat pipes721 via, for instance, thermal pads 722 and guide clips or springs 723.In one implementation, guide clips or springs 723 may comprise metalclips (or springs), rounded to guide the insertion of the adjoiningelectronic component(s) into its respective socket 705, and therebyfacilitate field-replaceability thereof.

As illustrated in the plan view of FIG. 7B, heat pipes 721 are (in oneembodiment) physically coupled, for instance, soldered or otherwisethermally attached, to enclosure 711. By way of example, pipe-receivingrecesses 724 may be formed in enclosure 711 to accommodate coupling ofrespective ends of heat pipe 721 to the enclosure 711, as illustrated.In this manner, good thermal conduction is provided from the heat pipesto the enclosure, which in one embodiment is itself thermallyconductive, for instance, being fabricated of metal. A plurality ofinwardly-extending, thermally conductive fins 725 may be provided,attached to or integrated with enclosure 711, in the regions where heatpipes 721 couple to enclosure 711 to facilitate convection of heat fromthe heat pipes to the dielectric fluid 714 within compartment 713 of theimmersion-cooled electronic component section 710.

In operation, as dielectric fluid absorbs heat in the immersion-cooledelectronic component section of the cooling apparatus, it undergoesphase change. This phase change utilizes the fluid's latent heat ofvaporization for cooling purposes. The resultant dielectric fluid vaporrises to the upper region of the compartment 713, where the fluid vaporcontacts the cool surfaces of the condenser fins 717 in the condensingregion. The condensing fins 717 are cooled by means of a thermalconduction coupling to the base of the liquid-cooled vapor condenser715, and further by convection to coolant (such as water) passingthrough the coolant-carrying channel(s) 716 of liquid-cooled vaporcondenser 715. Subsequent to making contact with the cooled condenserfin surfaces, the dielectric fluid vapor undergoes a second phase changeprocess from vapor to liquid state, and the resultant liquid dropsdownwards (due to gravity and its relatively higher density comparedwith the neighboring vapor region). By way of example, the thermallyconductive condenser fins 717 might comprise pin fin or plate finstructures. Further, depending on the implementation, the verticallength of the condenser fins may vary.

Simultaneously, heat is conducted from the field-replaceable electroniccomponents of the conduction-cooled electronic component section,through heat pipes 721 to enclosure 711, and subsequently transferred byconvection from the fins 725 to dielectric fluid 714 disposed withincompartment 713. Thus, in this implementation, the immersion-cooledelectronic component section, in addition to cooling the multipleelectronic components disposed within the immersion-cooled compartmentof that section, also facilitates dissipating heat thermally conductedfrom the conduction-cooled electronic component section to theenclosure.

As noted, and by way of example only, the field-replaceable electroniccomponents 703 of the conduction-cooled electronic component sectiondepicted in FIGS. 7A & 7B, may comprise dual-in-line memory modules(DIMMs) conduction-cooled via heat pipes attached at their edges to theimmersion-cooling enclosure of the immersion-cooled electronic componentsection of the cooling apparatus. As illustrated in these figures, theremaining electronic components of the electronic system are directlyimmersion-cooled via contact with the dielectric fluid. Thermalconduction to the heat pipes is facilitated by providing thermal padsattached to the opposing sides of the heat pipes using metal clips orsprings. The metal clips (or springs) facilitate smooth removal andinsertion of the respective DIMMs, without engaging edges of the heatpipe(s). (The use of a metal spring would also achieve a similarpurpose, while providing the added benefit of improved gap-filling.) Theheat pipes facilitate conducting heat from the DIMMs to theimmersion-cooled enclosure, where the heat is dissipated by convectionto the dielectric fluid within the compartment of the immersion-cooedelectronic component section.

As noted, FIGS. 8A-8C depict an alternate embodiment of a cooledelectronic system, generally denoted 700′, in accordance with one ormore aspects of the present invention. This cooled electronic system700′ is similar to cooled electronic system 700 described above inconnection with FIGS. 7A & 7B, with an exception being that the heatpipes 721 of the embodiment of FIGS. 7A & 7B are replaced byfluid-containing channels 800, coupled in fluid communication withcompartment 713 of the immersion-cooling electronic component section700. These fluid-containing channels 800 could be formed integral withenclosure 711 of the immersion-cooled electronic component section 710,or attached to the enclosure and aligned to respective openings in theenclosure, which allow dielectric fluid from the compartment into thefluid-containing channels.

Referring collectively to FIGS. 8A-8C, the conduction-cooled electroniccomponent section 720′, wherein field-replaceable electronic components703, 704 are provided, as explained above, includes (in this example)multiple fluid-containing channels 800, which comprise, in part,dielectric fluid 714 from compartment 713. These fluid-containingchannels 800 include sloped, upper surfaces 805, which facilitatedielectric vapor 802 egressing from the channels. As illustrated in FIG.8C, liquid dielectric fluid 714 enters the fluid channel(s), where itbecomes vaporized and exits as dielectric vapor 802. Vaporization occurswithin the fluid channel(s) 800 due to conduction of heat from theadjoining electronic components 703, 704 of the conduction-cooledelectronic component section 720′. In the example of FIGS. 8A-8C, thefluid-containing channels 800 are interleaved with the field-replaceableelectronic components, for instance, DIMMs.

As in the example described above in connection with FIGS. 7A & 7B,thermal pads 722 are provided, along with metal clips or springs 723, tofacilitate good thermal coupling between the removable,field-replaceable electronic components 703, 704, and thefluid-containing channels 800 coupled in fluid communication withcompartment 713 of the immersion-cooled electronic component section. Inthis implementation, as dielectric fluid 714 within the fluid-containingchannels 800 vaporizes due to transfer of heat from thefield-replaceable electronic components, the components are cooled. Thedielectric vapor 802 rises, and due to the sloped, upper surfaces 805 ofthe channels, is encouraged to flow upwards and outwards into the maincompartment 713, and subsequently to the liquid-cooled vapor condenser715, where it is condensed back into dielectric liquid. By sloping theupper surfaces of the fluid-containing channels 800, a circulation iscreated, where as dielectric vapor 802 flows outwards from thechannel(s) 800, it is replaced by new dielectric liquid 714 flowing intothe channel(s) from the compartment 713. In this embodiment, the thermalpads and metal clips/springs provide or facilitate gap-filling andthermal contact between the field-replaceable electronic components 703,704, and the dielectric fluid-containing channels 800.

FIGS. 9A-9C depict a further embodiment of a cooled electronic system700″, in accordance with one or more aspects of the present invention.This cooled electronic system is again similar to that described abovein connection with FIGS. 7A & 7B, with an exception being that the heatpipes 721 of that embodiment are replaced by a separable liquid-cooledcold plate 900. Referring collectively to FIGS. 9A-9C, in thisembodiment, liquid-cooled cold plate 900 includes a plurality ofthermally conductive fins 901, such as coolant-carrying fin structures,extending therefrom. Also, in this embodiment, the coolant-carryingchannels 716 of the liquid-cooled vapor condenser 715 of FIGS. 7A & 7B,are modified, for instance, enlarged, into a single flow path or channel716′ in the liquid-cooled vapor condenser 715′ of FIGS. 9A-9C.

With the depicted cooling approach, the field-replaceable electroniccomponents 703, 704 are first docked within their respective sockets 705mounted to electronics board 701, and then liquid-cooled cold plate 900is positioned over the electronic components, in fluid communicationwith the coolant-carrying channel 716′ of liquid-cooled condenser 715′of the immersion-cooled electronic component section of the coolingapparatus. As illustrated in FIG. 9A, in one embodiment, the thermallyconductive fins 901 which extend from the liquid-cooled cold plate 900comprise one or more coolant-carrying channels 902 disposed within therespective coolant-carrying fins structures. These fins 901 projectdownwards, into the space between the field-replaceable electroniccomponents 703, and are coupled in thermal communication with theelectronic components 703, 704, for instance, employing thermal pads 722and metal clips/springs 723, such as described above. However, note thatin this embodiment, the metal clips/springs 723 are inverted tofacilitate the insertion and removal of the liquid-cooled cold plate900, with the field-replaceable electronic components 703 alreadydisposed in operative position on electronics board 701.

As depicted in the partial cross-sectional view of FIG. 9C, fluidcommunication is achieved (in one embodiment) by interlockingliquid-carrying cold plate 900 with enclosure 711 such that thecoolant-carrying channel(s) 902 through liquid-cooled cold plate 900 isin fluid communication with the liquid-cooled channel 716′ ofliquid-cooled vapor condenser 715′ (see FIG. 9A). As shown in FIG. 9B,the secondary liquid coolant may be provided to the cooling apparatusvia a coolant inlet 910 and coolant outlet 911, coupled in fluidcommunication with the coolant-carrying channel 716′ of theliquid-cooled vapor condenser. In this embodiment, the coolant-carryingchannel 716′ of the liquid-cooled vapor condenser of theimmersion-cooled electronic component section 710′, is coupled in seriesfluid communication with the coolant-carrying channel(s) 902 of theliquid-cooled cold plate 900 associated with the conduction-cooledelectronic component section 720″. One or more O-ring seals 930 may beprovided at the interface between the liquid-cooled cold plate 900 andthe enclosure 711 to facilitate a fluid-tight connection between thecoolant-carrying channel 716′ of the liquid-cooled vapor condenser 715′,and the coolant-carrying channel(s) 902 of the coolant-cooled cold plate900.

Note that in operation, in this embodiment, heat is conducted from thefield-replaceable electronic components 703, 704, directly to thesecondary coolant, for instance, water, flowing through theliquid-cooled cold plate 900, and in order to field-replace anelectronic component from the conduction-cooled electronic componentsection 720″, the secondary coolant is first drained, the liquid-cooledcold plate 900 is removed, and then the field-replaceable electroniccomponent 703, 704 can be readily removed for servicing or replacement.Once the operation has been completed, the liquid-cooled cold plate 900is re-attached to the liquid-cooled vapor condenser of theimmersion-cooled electronic component section 710′ of the coolingapparatus. Attachment mechanisms, such as screws 920, may be employed tosecurely fasten the liquid-cooled cold plate to enclosure 711 of theimmersion-cooled electronic component section. Additional attachmentmechanisms (not shown) may be used at other points on the separableliquid-cooled cold plate 900, to secure it in position, for instance, tothe underlying electronics board 701, or to other points of thesurrounding enclosure 711 of the immersion-cooled electronic componentsection.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include” (and any formof include, such as “includes” and “including”), and “contain” (and anyform contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises”, “has”,“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises”, “has”, “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to best explain theprinciples of one or more aspects of the invention and the practicalapplication, and to enable others of ordinary skill in the art tounderstand one or more aspects of the invention for various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A cooled electronic system comprising: anelectronics board comprising a plurality of electronic componentsmounted to the electronics board; and a cooling apparatus facilitatingcooling of the plurality of electronic components mounted to theelectronics board, the cooling apparatus comprising: an immersion-cooledelectronic component section comprising: an enclosure at least partiallysurrounding and forming a compartment about multiple electroniccomponents of the plurality of electronic components mounted to theelectronics board; and a fluid disposed within the compartment, themultiple electronic components being, at least partially, immersedwithin the fluid to facilitate immersion-cooling thereof; and aconduction-cooled electronic component section, the conduction-cooledelectronic component section comprising at least one electroniccomponent of the plurality of electronic components mounted to theelectronics board, and the at least one electronic component beingindirectly liquid-cooled, at least in part, via conduction of heat fromthe at least one electronic component.
 2. The cooled electronic systemof claim 1, wherein the immersion-cooled electronic component sectionsurrounds the conduction-cooled electronic component section.
 3. Thecooled electronic system of claim 1, wherein the at least one electroniccomponent indirectly liquid-cooled in the conduction-cooled electroniccomponent section comprises at least one field-replaceable electroniccomponent.
 4. The cooled electronic system of claim 3, wherein the atleast one field-replaceable electronic component comprises at least onefield-replaceable memory module.
 5. The cooled electronic system ofclaim 1, wherein the conduction-cooled electronic component sectioncomprises at least one heat pipe and is physically coupled to theenclosure of the immersion-cooled electronic component section via theat least one heat pipe, the at least one heat pipe facilitating thermalconduction from the at least one electronic component of theconduction-cooled electronic component section to the enclosure of theimmersion-cooled electronic comment section, and via convection to thefluid disposed within the compartment of the immersion-cooled electroniccomponent section.
 6. The cooled electronic system of claim 5, whereinthe immersion-cooled electronic component section further comprises aliquid-cooled vapor condenser associated with the enclosure andfacilitating condensing of fluid vapor within the compartment, andthereby cooling of the multiple electronic components of theimmersion-cooled electronic component section, and indirectly, the atleast one electronic component of the conduction-cooled electroniccomponent section via thermal conduction from the at least oneelectronic component to the at least one heat pipe, and from the atleast one heat pipe to the enclosure of the immersion-cooled electroniccomponent section, and then via convection to the fluid within thecompartment.
 7. The cooled electronic system of claim 6, wherein theenclosure further comprises a plurality of thermally conductive finsprojecting into the compartment in a region where the conduction-cooledelectronic component section physically couples to the enclosure via theat least one heat pipe, the plurality of thermally conductive finsfacilitating transfer of heat, conducted from the at least one heat pipeto the enclosure, to the fluid within the compartment of theimmersion-cooled electronic component section.
 8. The cooled electronicsystem of claim 5, further comprising at least one thermal pad coupledto the at least one electronic component of the conduction-cooledelectronic component section, and disposed between the at least oneelectronic component of the conduction-cooled electronic componentsection and the at least one heat pipe, the at least one thermal padfacilitating conduction of heat from the at least one electroniccomponent to the at least one heat pipe.
 9. The cooled electronic systemof claim 1, wherein the enclosure of the immersion-cooled electroniccomponent section further comprises at least one fluid channel extendinginto the conduction-cooled electronic component section, and coupled influid communication with the compartment of the immersion-cooledelectronic component section, the at least one electronic component ofthe conduction-cooled electronic component section being coupled to theat least one fluid channel to facilitate thermal conduction of heat fromthe at least one electronic component of the conduction-cooledelectronic component section to the at least one fluid channel extendingfrom the enclosure of the immersion-cooled electronic component section.10. The cooled electronic system of claim 9, wherein theimmersion-cooled electronic component section further comprises aliquid-cooled vapor condenser associated with the enclosure andfacilitating condensing of fluid vapor within the compartment, andthereby cooling of the multiple electronic components of theimmersion-cooled electronic component section, and indirectly, the atleast one electronic component of the conduction-cooled electroniccomponent section via thermal conduction from the at least oneelectronic component to the at least one fluid channel extending fromthe enclosure of the immersion-cooled electronic component section, andhence to the fluid within the at least one fluid channel of theenclosure.
 11. The cooled electronic system of claim 10, wherein the atleast one fluid channel comprises at least one sloped surface whichfacilitates fluid vapor egressing from the at least one fluid channelinto the compartment, and hence, to the liquid-cooled vapor condenser ofthe immersion-cooled electronic component section.
 12. The cooledelectronic system of claim 1, wherein the conduction-cooled electroniccomponent section further comprises a liquid-cooled cold plate and atleast one thermally conductive fin extending from the liquid-cooled coldplate, the at least one electronic component of the conduction-cooledelectronic component section being coupled to the at least one thermallyconductive fin extending from the liquid-cooled cold plate to facilitatethermal conduction from the at least one electronic component of theconduction-cooled electronic component section to the liquid-cooled coldplate.
 13. The cooled electronic system of claim 12, wherein the atleast one thermally conductive fin extending from the liquid-cooled coldplate comprises at least one liquid-carrying fin structure extendingfrom the liquid-cooled cold plate, and wherein the immersion-cooledelectronic component section further comprises a liquid-cooled vaporcondenser associated with the enclosure and facilitating condensing offluid vapor within the compartment, and thereby cooling of the multipleelectronic components of the immersion-cooled electronic componentsection, the liquid-cooled cold plate and the liquid-cooled vaporcondenser being coupled in fluid communication.
 14. The cooledelectronic system of claim 13, wherein the liquid-cooled vapor condenserand the liquid-cooled cold plate are coupled in series fluidcommunication.
 15. The cooled electronic system of claim 13, whereinliquid coolant flows through a first portion of the liquid-cooled vaporcondenser, then through the liquid-cooled cold plate, before flowingthrough a second portion of the liquid-cooled vapor condenser.
 16. Aliquid-cooled electronics rack comprising: an electronics rackcomprising at least one electronic system, the at least one electronicsystem comprising an electronics board including a plurality ofelectronic components mounted to the electronics board; and a coolingapparatus comprising: an immersion-cooled electronic component section,the immersion-cooled electronic component section comprising: anenclosure at least partially surrounding and forming a compartment aboutmultiple electronic components of the plurality of electronic componentsmounted to the electronics board; and a fluid disposed within thecompartment, the multiple electronic components being, at leastpartially, immersed within the fluid to facilitate immersion-coolingthereof; and a conduction-cooled electronic component section, theconduction-cooled electronic component section comprising at least oneelectronic component of the plurality of electronic components mountedto the electronics board, and the at least one electronic componentbeing indirectly liquid-cooled, at least in part, via conduction of heatfrom the at least one electronic component.
 17. The liquid-cooledelectronics rack of claim 16, wherein the immersion-cooled electroniccomponent section surrounds the conduction-cooled electronic componentsection.
 18. The liquid-cooled electronics rack of claim 16, wherein theat least one electronic component indirectly liquid-cooled in theconduction-cooled electronic component section comprises at least onefield-replaceable electronic component.
 19. The liquid-cooledelectronics rack of claim 16, wherein the conduction-cooled electroniccomponent section comprises at least one heat pipe and is physicallycoupled to the enclosure of the immersion-cooled electronic componentsection via the at least one heat pipe, the at least one heat pipefacilitating thermal conduction from the at least one electroniccomponent of the conduction-cooled electronic component section to theenclosure of the immersion-cooled electronic component section, and viaconvection to the fluid disposed within the compartment of theimmersion-cooled electronic component section.
 20. The liquid-cooledelectronics rack of claim 19, wherein the immersion-cooled electroniccomponent section further comprises a liquid-cooled vapor condenserassociated with the enclosure and facilitating condensing of fluid vaporwithin the compartment, and thereby cooling of the multiple electroniccomponents of the immersion-cooled electronic component section, andindirectly, the at least one electronic component of theconduction-cooled electronic component section via thermal conductionfrom the at least one electronic component to the at least one heatpipe, and from the at least one heat pipe to the enclosure of theimmersion-cooled electronic component section, and then via convectionto the fluid within the compartment.
 21. The liquid-cooled electronicsrack of claim 16, wherein the enclosure of the immersion-cooledelectronic component section further comprises at least one fluidchannel extending into the conduction-cooled electronic componentsection and coupled in fluid communication with the compartment of theimmersion-cooled electronic component section, the at least oneelectronic component of the conduction-cooled electronic componentsection being coupled to the at least one fluid channel to facilitatethermal conduction of heat from the at least one electronic component ofthe conduction-cooled electronic component section to the at least onefluid channel extending from the enclosure of the immersion-cooledelectronic component section.
 22. The liquid-cooled electronics rack ofclaim 21, wherein the immersion-cooled electronic component sectionfurther comprises a liquid-cooled vapor condenser associated with theenclosure and facilitating condensing of fluid vapor within thecompartment, and thereby cooling of the multiple electronic componentsof the immersion-cooled electronic component section, and indirectly,the at least one electronic component of the conduction-cooledelectronic component section via thermal conduction from the at leastone electronic component to the at least one fluid channel extendingfrom the enclosure of the immersion-cooled electronic component section,and hence to the fluid within the at least one fluid channel of theenclosure.
 23. The liquid-cooled electronics rack of claim 16, whereinthe conduction-cooled electronic component section further comprises aliquid-cooled cold plate and at least one thermally conductive finextending from the liquid-cooled cold plate, the at least one electroniccomponent of the conduction-cooled electronic component section beingcoupled to the at least one thermally conductive fin extending from theliquid-cooled cold plate to facilitate thermal conduction from the atleast one electronic component of the conduction-cooled electroniccomponent section to the liquid-cooled cold plate.
 24. The liquid-cooledelectronics rack of claim 23, wherein the at least one thermallyconductive fin extending from the liquid-cooled cold plate comprises atleast one liquid-carrying fin structure extending from the liquid-cooledcold plate, and wherein the immersion-cooled electronic componentsection further comprises a liquid-cooled vapor condenser associatedwith the enclosure and facilitating condensing of fluid vapor within thecompartment, and thereby cooling of the multiple electronic componentsof the immersion-cooled electronic component section, the liquid-cooledcold plate and the liquid-cooled vapor condenser being coupled in fluidcommunication.